Exam 3 questions/concepts

Question 1

Give two examples of second messengers, how it is generated and what it does.

Answer 1

1. cAMP: generated by adenine cyclase in response to active Galpha subunit of heterotrimeric G protein, targets regulatory subunits of PKA.
2. IP3: generated by PLC cleaving PIP2 in response to active Galpha subunit, target a ligand gated Calcium channel on ER.

Question 2

Explain how EGF signaling is transmitted from the cytosol to the nucleus.

Answer 2

1. EGF binds EGF receptor: dimerizes = transautophosphorylation.
2. Grb2: adaptor protein binds phosphorylated tyrosine.
3. SOS : GEF for Ras binds Brb2, SOS facilitates exchange of GDP to GTP on Ras (now active)
4. Ras recruits Raf (Raf is phosphorylated, but not by Ras, G proteins are NOT KINASES)
5. Raf-MEK-ERK cascade
6. ERK: NLS exposed when phosphorylated = enters the nucleus to phosphorylate TFs.

Question 3

What regulates gap junctions?

Answer 3

2 Connexons form a Ca++ inducible, hydrophilic channel that allows for chemical communication. Excess Calcium closes the channel.

Question 4

What are 3 KEY functions of MTs?

Answer 4

1. They form roads for kinesin and dynein motors to shuttle cargo their destinations.
2. They form the mitotic spindle and central spindle while mediating cell division.
3. They are polar structures that provide an orientation for anterograde or retrograde motors.

Question 5

Some MAPs ____ ______ _____ MTs.

Answer 5

Stabilize, others destabilize or sever MTs

Question 6

The motor domain of minus-end directed kinesins are at the ____ end of the polypeptide chain?

Answer 6

C-terminal

Question 7

How are gamma-TUSC and TURC involved in MTOC?

Answer 7

Gamma-TUSC (g-tubulin small complex) is a part of the gamma-TURC (g-tubulin Ring complex). Seven g-TUSC’s form the template for a 13 protofilament MT.

Question 8

What characterizes a processive motor?

Answer 8

It may travel along MTs on its own for long distances.